Image processing that removes the background color included in an original image is known. In this processing, the luminance (or density) histogram of an image scanned by a scanner is generated, and the background signal level (to be referred to as “background level” hereinafter) of the original image is detected based on the histogram. The background level is subtracted from an image signal, thus removing the background from the image (to be referred to as “background removal” hereinafter).
Japanese Patent Laid-Open No. 2000-022971 discloses a technique which calculates a background removal amount according to the signal level of an image signal and varies the background removal amount according to the signal level of the image signal in place of simply subtracting the background level from the image signal.
However, in these techniques, when all pixels of an original image are selected to generate a histogram, a huge memory capacity is required. For this reason, it is a common practice to use discretely sampled pixels to generate a histogram. As a result, the histogram is readily influenced by a dust image or noise included in the original image, and the background cannot be accurately read.
When the background level is determined based on the luminance (or density) distribution pattern after the histogram is generated, and that of a clip or the like of a newspaper or magazine pasted on a white sheet is to be detected, white of the white sheet is detected as a background, and the background of the clip to be originally removed cannot be removed.